Paired, active-space treatments of static correlation are augmented with additional amplitudes to produce a hierarchy of parsimonious and efficient cluster truncations that approximate the total energy. The number of parameters introduced in these models grow with system size in a tractable way: two powers larger than the static correlation model it is built upon: for instance cubic for the models built on perfect pairing, fourth order for a perfect quadruples (PQ) reference, and fifth order for the models built on perfect hextuples. These methods are called (SD) corrections to perfect pairing, PQ, perfect hextuples, and two variants are explored. An implementation of the SD methods is compared to benchmark results for and dissociation problems, the and model systems, and the insertion of beryllium into hydrogen. In the cases examined even the quartic number of parameters associated with PQSD is able to provide results which meaningfully improve on coupled-cluster singles doubles (CCSD) (which also has quartic amplitudes) and compete with existing multi-reference alternatives.
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28 September 2010
Research Article|
September 23 2010
A truncation hierarchy of coupled cluster models of strongly correlated systems based on perfect-pairing references: The models
John A. Parkhill;
John A. Parkhill
a)
Department of Chemistry,
University of California
, Berkeley, California 94720, USA
and Chemical Sciences Division, Lawrence Berkeley National Laboratory
, Berkeley, California 94720, USA
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Martin Head-Gordon
Martin Head-Gordon
a)
Department of Chemistry,
University of California
, Berkeley, California 94720, USA
and Chemical Sciences Division, Lawrence Berkeley National Laboratory
, Berkeley, California 94720, USA
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a)
Electronic addresses: john.parkhill@gmail.com and mhg@cchem.berkeley.edu. Tel.: 510-642-5957. FAX: 510-643-1255.
J. Chem. Phys. 133, 124102 (2010)
Article history
Received:
May 20 2010
Accepted:
August 02 2010
Citation
John A. Parkhill, Martin Head-Gordon; A truncation hierarchy of coupled cluster models of strongly correlated systems based on perfect-pairing references: The models. J. Chem. Phys. 28 September 2010; 133 (12): 124102. https://doi.org/10.1063/1.3483556
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